Third time's the charm.

After years of debate, two rejected sites and immeasurable frustration, plans for the Museum of the American Revolution are finally under way, with the announcement Tuesday that the architect chosen to design the museum is - again - Robert A.M. Stern.

"The institution is incredibly important," Stern said. "It's a thrill to be part of the process."

And, no doubt, a test of patience.

The New York architect, longtime dean of the Yale School of Architecture, has been selected twice before to design the museum - first in 2004, when it was to be built in Valley Forge National Historical Park, and a year later, when the site was moved to an adjacent property.

Both projects were scrapped when disputes arose with the National Park Service, neighbors, and other parties over the museum's placement and potential ancillary land use.

Then, last year, the American Revolution Center, the nonprofit creating the museum and supplying its artifacts, agreed to give the Park Service a 78-acre property across from Valley Forge in exchange for the site of the old Independence Park visitor center at Third and Chestnut Streets.

Although Stern's firm might have seemed the automatic choice for the new project, the center sought competitive bids once more.

"We felt that in order to exercise due diligence, we should go out there," said David Acton, secretary of the center's board of directors and vice chairman of the building committee that reviewed 40 architects' proposals.

Last spring, five finalists were chosen. Stern's concept was the clear winner, Acton said: "Bob took it to a higher level. His conceptual proposal was very detailed."

Stern's concept for the museum at Valley Forge was praised for its sophistication and fluid lines.

The building on Independence Mall will be very different, Acton said: "It is in a city district as opposed to a cornfield. If they had just rehashed the old design, we wouldn't have been impressed."

The $150 million project, funded in part with a grant from the state, is expected to be completed in 2015. Stern, in an interview, anticipated that he would have a "fully cooked" design ready by February.

His firm designed the Comcast Center and plans for the redevelopment of the Navy Yard. Among the other buildings in the 72-year-old architect's portfolio are the Norman Rockwell Museum in Stockbridge, Mass.; hotels for the Walt Disney Co. in Orlando, Paris, and Tokyo; and the George W. Bush Presidential Center at Southern Methodist University in Dallas.

Despite his success, critics have faulted some of Stern's work. Inquirer architecture critic Inga Saffron once wrote that he had a reputation of "serving up bland historical pastiches."

"I feel a great sense of responsibility," Stern said last week. The new three-story museum will sit east of Independence Hall, "cheek by jowl" with the Custom House, he said. "It will be a small building at the foothill of a mountain."

Unlike the modernist National Museum of American Jewish History, which opened on the mall last year, Stern said, his design will use "the language of traditional Philadelphia architecture." He plans to work with red brick and limestone, and perhaps wooden windows: "We will make an inventive new composition using those familiar elements."

The interior will feature a grand staircase and entrance lobby that will prepare visitors to imagine going back to the revolutionary period, he said.

"It's one of the great commissions that I've ever undertaken," Stern said.

Among the items in the center's collection, much of which has been kept in storage for years, are a tent of George Washington's, a 1777 bill of sale for an 18-year-old slave named Henry from New Jersey, and a brace of silver-mounted cannon-barrel pistols that once belonged to Lord North, British prime minister under King George III.

The center also announced that the exhibits will be designed by MFM Design, a Maryland firm that has done projects for the Smithsonian Institution, Winterthur, and the American Museum of Natural History.

H.F. "Gerry" Lenfest, chairman of the center's board, said in a statement that both Stern's firm and MFM were chosen through a rigorous process. "In their distinct disciplines," he said, "each firm has the expertise to lead our efforts to develop a world-class museum that will inspire and engage people."